scholarly journals HYDROMECHANICAL BEHAVIOUR OF TWO UNSATURATED SILTS: LABORATORY DATA AND MODEL PREDICTIONS

2021 ◽  
Author(s):  
Agostino Walter Bruno ◽  
Domenico Gallipoli ◽  
Joao Mendes
Keyword(s):  
Water Content ◽  
Laboratory Data ◽  
Degree Of Saturation ◽  
Model Parameters ◽  
Clayey Silt ◽  
Constant Suction ◽  
Observed Behaviour ◽  
Hydromechanical Behaviour ◽  
Soil Behaviour ◽  
Hydromechanical Model

This paper presents the results from a campaign of unsaturated and saturated isotropic tests performed on two compacted silts of different coarseness, namely a clayey silt and a sandy silt, inside triaxial cells. Some tests involved an increase/decrease of mean net stress at constant suction or an increase/decrease of suction at constant mean net stress. Other tests involved an increase of mean net stress at constant water content with measurement of suction. During all tests, the void ratio and degree of saturation were measured to investigate the mechanical and retention behaviour of the soil. The experimental results were then simulated by the bounding surface hydromechanical model of Bruno and Gallipoli (2019), which was originally formulated to describe the behaviour of clays and clayey silts. Model parameters were calibrated against unsaturated tests including isotropic loading stages at constant water content with measurement of varying suction. Loading at constant water content is relatively fast and allows the simultaneous exploration of large ranges of mean net stress and suction, thus reducing the need of multiple experiments at distinct suction levels. Predicted data match well the observed behaviour of both soils, including the occurrence of progressive yielding and hysteresis, which extends the validation of this hydromechanical model to coarser soils. Specific features of the unsaturated soil behaviour, such as wetting-induced collapse, are also well reproduced.

Compacted soil behaviour through changes of density, suction, and stiffness of soils with remoulding water content

2018 ◽  
Vol 55 (2) ◽  
pp. 182-190 ◽  
Author(s):  
T.W. Zhang ◽  
Y.J. Cui ◽  
F. Lamas-Lopez ◽  
N. Calon ◽  
S. Costa D’Aguiar
Keyword(s):  
Water Content ◽  
Dry Density ◽  
Soil Plasticity ◽  
Optimum Water Content ◽  
Hydromechanical Behaviour ◽  
The Difference ◽  
Two Peaks ◽  
Soil Behaviour ◽  
Optimum Water ◽  
Water Contents

To better understand the overall hydromechanical behaviour of interlayer soil, the compaction behaviour of one of the two components — the portion of fines (<4 mm) that is sensitive to water content changes — was investigated. The standard Proctor compaction curves were first determined for the soils. Then, the maximum shear modulus, Gmax, and suction were measured on samples statically compacted at an identical dry density, but different remoulding water contents. The changes in Gmax reveal the existence of a characteristic water content corresponding to the maximum Gmax. The results also show that this characteristic water content increases with the soil plasticity, being similar to the variation trend of optimum water content with soil plasticity. A bimodal pattern was observed from the plot of total suction ψ versus the slope of water content w–log(ψ) curve. The suction corresponding to the maximum Gmax is close to the lowest point between the two peaks in the ψ–dw/dlog(ψ) curve. A reasonable explanation was attempted for the correspondence between the “optimum water content” defined by the maximum value of Gmax and the corresponding suction. The difference between the static and dynamic compactions was also explained in terms of suction values.

scholarly journals Dilatancy Characteristics and Constitutive Modelling of the Unsaturated Soil Based on Changes in the Mass Water Content

2021 ◽  
Vol 11 (11) ◽  
pp. 4859
Author(s):  
Xiao Xu ◽  
Guoqing Cai ◽  
Zhaoyang Song ◽  
Jian Li ◽  
Chongbang Xu ◽  
...  
Keyword(s):  
Water Content ◽  
Unsaturated Soil ◽  
Soil Mechanics ◽  
Constitutive Models ◽  
Confining Pressure ◽  
Prediction Equation ◽  
Constitutive Modelling ◽  
Degree Of Saturation ◽  
Model Parameters ◽  
High Plasticity

Most soil mechanics theories are limited to strain hardening and shrinkage under high compressive stresses, and there are some shortcomings in the selection of suction or degree of saturation as the water content state varies in the constitutive models of unsaturated soil. Based on the triaxial shear tests of unsaturated compacted soil (a silt of high plasticity) with different water content and confining pressure (low-confining), a shear dilatancy model of unsaturated soil based on the mass water content is proposed in this paper. The influence of the water content on the shear deformation characteristics of the unsaturated soil is analysed. The stress–dilatancy relationship and the prediction equation of the minimum dilatancy rate of the unsaturated soil under different water content and different confining pressure are provided. Selecting the mass water content as the state variable, a constitutive model suitable for the dilatancy of unsaturated soil is established. The method of determining model parameters based on the mass water content is analysed. The applicability of the model is verified by comparisons between the predicted and experimental results.

scholarly journals A microstructure-based elastoplastic model to describe the behaviour of a compacted clayey silt in isotropic and triaxial compression

2020 ◽  
Vol 57 (7) ◽  
pp. 1025-1043 ◽  
Author(s):  
Guido Musso ◽  
Arash Azizi ◽  
Cristina Jommi
Keyword(s):  
Water Retention ◽  
Triaxial Compression ◽  
Double Porosity ◽  
Degree Of Saturation ◽  
Water Retention Capacity ◽  
Flow Rule ◽  
Retention Capacity ◽  
Clayey Silt ◽  
Hydromechanical Behaviour ◽  
As Stress

The paper focuses on the hydromechanical behaviour of an unsaturated compacted clayey silt, accounting for fabric changes induced by drying–wetting cycles occurring at low stress levels. The response along isotropic compression and triaxial compression (shear) at constant water content was investigated by laboratory tests on both as-compacted and dried–wetted samples. Compaction induces a microstructural porosity pertinent to clay peds and a macrostructural porosity external to the peds. Drying–wetting cycles decrease the microporosity and increase the macroporosity, which reduces the water retention capacity, increases the compressibility, and promotes higher peak strengths with more brittle behaviour during triaxial compression. A coupled double-porosity elastic–plastic model was formulated to simulate the experimental results. A nonassociated flow rule was defined for the macrostructure, modifying a stress–dilatancy relationship for saturated granular soils to account for the increase in dilatancy with suction observed in the experiments. The average skeleton stress and suction were adopted as stress variables. As correctly predicted by the model, the shear strength at critical state is not significantly influenced by the degree of saturation or by the hydraulic history. On the contrary, the higher peak strength, brittleness, and dilatancy of the dried–wetted samples are mostly explained by their reduced water-retention capacity.

Coupling hydraulic with mechanical models for unsaturated soils

2011 ◽  
Vol 48 (5) ◽  
pp. 826-840 ◽  
Author(s):  
Daichao Sheng ◽  
An-Nan Zhou
Keyword(s):  
Unsaturated Soils ◽  
Constitutive Relations ◽  
Volumetric Strain ◽  
Degree Of Saturation ◽  
Coupling Mechanism ◽  
Proposed Model ◽  
Mechanical Models ◽  
Hydromechanical Behaviour ◽  
Soil Behaviour ◽  
Different Soils

This paper presents an alternative method to couple the hydraulic component with the mechanical component in a constitutive model for unsaturated soils. Some pioneering work on hydromechanical coupling is reviewed. Generalized constitutive relations on coupled hydromechanical behaviour are introduced. These generalized constitutive relations are then incorporated into existing mechanical and hydraulic models for unsaturated soils. A new coupling mechanism is proposed based on the fact that soil-water characteristic equations are usually obtained for constant stress, not constant volume. The proposed coupling mechanism also satisfies the intrinsic relationship between the degree of saturation and the volumetric strain for undrained compression. Numerical examples are presented to show the performance of the proposed model in predicting soil behaviour along drying and loading paths. Finally, the model is validated against experimental data for different soils.

Experimental study on volumetric behaviour of Maryland clay and the role of degree of saturation

2014 ◽  
Vol 51 (12) ◽  
pp. 1449-1455 ◽  
Author(s):  
Glen J. Burton ◽  
Daichao Sheng ◽  
David Airey
Keyword(s):  
Water Content ◽  
State Parameter ◽  
Degree Of Saturation ◽  
State Variable ◽  
Optimum Water Content ◽  
Constant Suction ◽  
Compaction Energy ◽  
Oedometer Tests ◽  
Compression Line

In this paper, the volume change behaviour of Maryland clay compacted on the wet side of standard Proctor optimum water content (with lower compaction energy) is studied in reference to the saturated reconstituted state. Oedometer tests over a range of suctions and vertical stresses have been carried out, and the results have shown that the compression index reaches a peak (approximately twice that of the reconstituted material) and then gradually reduces to the reconstituted value as the stress level is increased. The results are analyzed in a framework where the degree of saturation is treated as a state parameter and controls the slope of the unsaturated normal compression line. Tests conducted under constant suction and constant water content have been used to demonstrate the effectiveness of using the degree of saturation as a state variable.

scholarly journals Determination of Field Capacity in a Florida Sandy Soil and Drainage Time at Different Depths

1999 ◽  
Vol 9 (2) ◽  
pp. 258-261 ◽  
Author(s):  
Mongi Zekri ◽  
Lawrence R. Parsons
Keyword(s):  
Water Content ◽  
Soil Water ◽  
Soil Water Content ◽  
Laboratory Data ◽  
Field Capacity ◽  
Fine Sand ◽  
Degree Of Saturation ◽  
Undisturbed Soil ◽  
Different Depths

The development of improved equipment for measuring soil water content has created the need for a better understanding of soil water drainage and movement. Without this understanding, it is impossible to know if an observed decrease in soil water content at a particular depth is due to evapotranspiration and/or continual drainage. This study was designed to determine the length of time for different soil depths of a Florida Candler fine sand to reach field capacity. A field site with no vegetation on it was saturated with water and covered with a plastic tarp to prevent evaporation. At 6- to 24-hour intervals, soil water content was measured gravimetrically in the top 15 cm (6 inches) and with the neutron probe from 30 to 150 cm (12 to 59 inches). The 15-cm depth reached field capacity after one day, but it took 4 days for the 30- to 150-cm depths to reach field capacity because of rewetting by water draining form higher horizons. The time required for drainage to stop must be considered when evaluating changes in soil water status at a particular depth. This is important for distinguishing between plant water uptake and drainage for different soil layers.Soil water characteristic curves of undisturbed soil samples, bulkdensity, porosity, and field capacity in situ were also determined for this soil. Field capacity values found in situ were compared to those found using the pressure plate technique. Laboratory values were higher than field values because the laboratory data were closer to hydrostatic conditions than the field data and the degree of saturation provided during wetting of the cores was higher in the laboratory. Water was not readily retained in Candler fine sand because the soil was very porous, infiltration rates were high, drainage was rapid, and water storage capacity was limited. Using field measurements, field capacity values of soil at different depths ranged from 4.8% to 6.2% volume for Candler fine sand. These are considered to be low values when compared to other types of soil.

scholarly journals Mechanical behavior of an unsaturated clayey silt: an experimental and constitutive modelling study

2019 ◽  
Vol 56 (10) ◽  
pp. 1461-1474
Author(s):  
Enrique Romero ◽  
Marcelo Sánchez ◽  
Xuerui Gai ◽  
Mauricio Barrera ◽  
Antonio Lloret
Keyword(s):  
Triaxial Compression ◽  
Constitutive Modelling ◽  
Triaxial Tests ◽  
Model Parameters ◽  
Compression Tests ◽  
Stress Strain ◽  
Hardening Law ◽  
Clayey Silt ◽  
Constant Suction ◽  
Realistic Description

This paper reports an experimental study and subsequent constitutive modelling focused on the stress-strain and volumetric responses during deviatoric stress application of a partially saturated clayey silt. The material was statically and isotropically compacted at constant water content towards a pre-defined pre-consolidation stress. A series of strain-controlled triaxial compression tests on a state of the art device and isotropic experiments are presented and discussed. The triaxial tests started at the same stress state (i.e., identical matric suction and mean net stress) and were conducted at the same constant suction. Several stress paths under isotropic conditions (i.e., drying–wetting, loading–unloading, and wetting–drying) were followed to induce different overconsolidated states before shearing the specimens. The test results are initially interpreted using the elastoplastic Barcelona Basic Model (BBM). Independent tests were selected to determine the model parameters associated with the volumetric behavior of the soil. The BBM was not able to capture the dilatant behavior observed during shearing. An enhancement of the BBM is proposed in this work, which includes both, a more general hardening law and sub-loading concepts. The main capabilities and limitations of the original BBM and the enhanced model are discussed and compared. The modified BBM was able to handle the dilatancy observed in the experiments and provided a more realistic description of the experimental stress-strain response.

Inclusion of specific water volume within an elasto-plastic model for unsaturated soil

1996 ◽  
Vol 33 (1) ◽  
pp. 42-57 ◽  
Author(s):  
S J Wheeler
Keyword(s):  
Water Content ◽  
Unsaturated Soil ◽  
Critical State ◽  
Constitutive Models ◽  
Degree Of Saturation ◽  
Triaxial Tests ◽  
Water Volume ◽  
Plastic Model ◽  
Elasto Plasticity ◽  
Soil Behaviour

Existing elasto-plastic critical state constitutive models for unsaturated soil provide no information on the variation of water content or degree of saturation. These models cannot therefore, for example, be used to predict unsaturated soil behaviour during undrained loading, when the variation of suction is determined by the requirement that water content remains constant. This problem has been tackled by extending an existing elasto-plastic model to include relationships describing the variation of specific water volume (the volume of water and solids in an element of soil containing unit volume of solids). The proposed form of the variation of specific water volume was based on consideration of the soil fabric, resulting in a coupled form of elasto-plastic behaviour. Predictions from the elasto-plastic model showed good agreement with the experimental results from suction-controlled triaxial tests on unsaturated samples of compacted speswhite kaolin. Normal compression lines for specific water volume at different values of suction were well predicted, as was the variation of specific water volume during wetting. Critical state values of specific water volume were slightly underestimated, but test paths for both drained and undrained shearing were predicted with reasonable success. Key words: compacted clays, constitutive model, critical state, elasto-plasticity, triaxial tests, unsaturated.

scholarly journals Temporal stability of electrical conductivity in a sandy soil

2016 ◽  
Vol 30 (3) ◽  
pp. 349-357 ◽  
Author(s):  
Aura Pedrera-Parrilla ◽  
Eric C. Brevik ◽  
Juan V. Giráldez ◽  
Karl Vanderlinden
Keyword(s):  
Electrical Conductivity ◽  
Spatial Variability ◽  
Water Content ◽  
Soil Water ◽  
Soil Water Content ◽  
Precision Agriculture ◽  
Temporal Stability ◽  
Principal Component ◽  
Model Parameters ◽  
Soil Spatial Variability

Abstract Understanding of soil spatial variability is needed to delimit areas for precision agriculture. Electromagnetic induction sensors which measure the soil apparent electrical conductivity reflect soil spatial variability. The objectives of this work were to see if a temporally stable component could be found in electrical conductivity, and to see if temporal stability information acquired from several electrical conductivity surveys could be used to better interpret the results of concurrent surveys of electrical conductivity and soil water content. The experimental work was performed in a commercial rainfed olive grove of 6.7 ha in the ‘La Manga’ catchment in SW Spain. Several soil surveys provided gravimetric soil water content and electrical conductivity data. Soil electrical conductivity values were used to spatially delimit three areas in the grove, based on the first principal component, which represented the time-stable dominant spatial electrical conductivity pattern and explained 86% of the total electrical conductivity variance. Significant differences in clay, stone and soil water contents were detected between the three areas. Relationships between electrical conductivity and soil water content were modelled with an exponential model. Parameters from the model showed a strong effect of the first principal component on the relationship between soil water content and electrical conductivity. Overall temporal stability of electrical conductivity reflects soil properties and manifests itself in spatial patterns of soil water content.

Using time domain reflectometry in triaxial testing

2000 ◽  
Vol 37 (6) ◽  
pp. 1325-1331
Author(s):  
J LH Grozic ◽  
M E Lefebvre ◽  
P K Robertson ◽  
N R Morgenstern
Keyword(s):  
Cyclic Loading ◽  
Water Content ◽  
Time Domain ◽  
Void Ratio ◽  
Time Domain Reflectometry ◽  
Volumetric Water Content ◽  
Degree Of Saturation ◽  
Triaxial Testing ◽  
Empirical Correlations ◽  
Static And Cyclic Loading

Time domain reflectometry (TDR) can be used to determine the volumetric water content of soils. This note describes the utilization of a TDR miniprobe in triaxial testing. The TDR performance was examined with a series of tests that not only proved its reliability but also resulted in two empirical correlations. Using these correlations, the degree of saturation and volumetric water content during triaxial testing could be determined. The TDR was then put to use in a laboratory program designed to investigate the response of loose gassy sand under static and cyclic loading. Because of the TDR measurements it was possible to determine the degree of saturation and void ratio of the gassy specimens. The TDR miniprobe proved to be accurate, simple to use, and inexpensive to build.Key words: time domain reflectometry, TDR, triaxial testing, gassy, unsaturated.

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